1. Field of the Invention.
This invention relates to apparatus and methods for quantitatively determining the amount of volatile products and solvents remaining in a material after manufacture and, more particularly, to determining the amount of the specific solvent N-methyl-2-pyrrolidone (NMP) in resin pre-impregnated fabric ("prepreg").
2. Description of the Related Art.
In the present context, pre-impregnation refers to the coating of a reinforcing material or substrate with a resin before molding takes place. "Prepreg" is a term for the reinforcing material that contains or is combined with the full complement of resin before the molding operation.
Gas chromatography is a method of separating and analyzing mixtures of liquid or gaseous chemical substances by adsorption, which is a preferential adsorption of specific chemical compounds (in the gas phase) onto a solid or solid-liquid adsorbent material to achieve separation of components present therein.
Previously it has not been possible to monitor the amount of high-boiling-point solvent NMP present in polyimide impregnated fabric. Heretofore the volatile content tests that have been performed have evolved reactive volatiles (specifically ethanol and water) plus a variable amount of the non-reactive volatiles (NMP) present.
The amount of solvent retained in prepreg after manufacture is a critical parameter which directly affects the success of subsequent operations to produce finished parts from the prepreg. The art associated with test methods in the areas of process and quality control for solvated condensation-curing resin prepregs would be greatly benefited by a test method which evolves all reactive and non-reactive volatiles from prepreg test specimens and permits quantitative analysis of the amounts of individual chemical species in the condensate. It would also be valuable if such a test method included an internal check on collection efficiency to insure that the results obtained were accurate. Such a test method would provide a basis for determination of the levels of reactive and non-reactive volatiles retained in other solvated condensation-curing resin systems employing other solvents (e.g., methanol, ethanol, benzene, toluene, xylene, diglyme, etc.) as well as other types of condensation-curing resin systems (e.g., phenolics, various other polyimides, polybenzimidazoles, etc.).
General background information about gas chromatography and examples of the related art are given in the following U.S. patents and other publications.
U.S. Pat. No. 3,169,389 to Green, Jr. et al describes a method and means for gas chromatographic analysis adapted to resolve a sample mixture into fractions having similar boiling points.
U.S. Pat. No. 3,171,274 to Loyd describes a method and apparatus for gas chromatographic analysis entailing a vaporizing and sampling method for analysis of a liquid which normally tends to polymerize upon heating.
U.S. Pat. No. 3,171,722 to Natelson describes a gas extractor and ejector for use in gas chromatography which provide an arrangement for the separation of gases and liquids. Precise quantities of gases are fed to a gas chromatograph device to analyze very small quantities of gas. Samples of consistent quantity and volume are provided with the objective of obtaining consistent results on a gas chromatograph device.
U.S. Pat. No. 3,372,573 to Sanford et al describes a method and apparatus for chromatographic analysis comprising a valving system with three sequentially operating control units to provide an improved method and apparatus for obtaining a vaporous sample from a liquid containing a soluble non-volatile constituent.
U.S. Pat. No. 3,407,647 to Lynn describes a system which provides a vaporized sample to a gas chromatography column via a vaporizing chamber into which the sample is forced under high pressure, then vaporized and carried into the column by a low-pressure carrier gas.
U.S. Pat. No. 3,779,066 to Fore et al describes a method and means for gas chromatographic analysis of residual solvents and acetone dimers in oil seed meals and flours.
U.S. Pat. No. 3,889,538 to Fingerle describes a method and means for introducing a small sample of a volatile liquid into the carrier gas stream of a gas chromatography unit.
U.S. Pat. No. 3,996,003 to Fine et al describes a liquid chromatograph system for detecting N-nitroso compound content in specific samples.
U.S. Pat. No. 4,335,620 to Adams describes a temperature controlled sample carrier apparatus suitable for use in liquid chromatography systems.
U.S. Pat. No. 4,452,067 to Ahlstrom, Jr., et al describes a method and means for gas chromatographic vapor phase analysis of process streams containing condensible and non-condensible phases variously comprising hydrogen, water, oxides of carbon, aliphatic hydrocarbons, and aromatic hydrocarbons.
The article "An Injection System For Gas Chromatography" by Nawar et al in Analytical Chemistry, Volume 32, No. 11, October, 1960, describes a sample volatilization and injection system for a gas chromatography unit.
The article "Gas Chromatography of Volatiles From Breath And Urine" by Teranishi et al in Analytical Chemistry (USA), Volume 44, No. 1, Jan. 1972, describes a technique for gas chromatographic analysis of volatiles from human breath and urine.
The article "Analysis of Fixed And Condensible Gases by Two-Stage Gas Chromatography" by Madison in Analytical Chemistry, Volume 30, No. 11, Nov. 1958, describes a two-stage gas chromatographic analysis method for mixtures of fixed and condensible gases.
The article "Gas Chromatographic Estimation of Occluded Solvents in Adhesive Tapes by Periodic Introduction Method" in Analytical Chemistry (USA), Volume 42, No. 14, Dec. 1970, by Suzuki describes a method and apparatus for gas chromatographic analysis of occluded solvents in coated materials such as adhesive tape via a vaporizing attachment connected to the inlet port of a gas chromatographic unit.